Metal-insulator transition in monolayer MoS2 via contactless chemical doping

Camiel Van Efferen,Jeison Fischer,Thomas Michely,Wouter Jolie,Hannu-Pekka Komsa,Clifford Murray,Carsten Busse

doi:10.1088/2053-1583/ac5d0f

Camiel Van Efferen, Jeison Fischer + Show 5 more

Open Access

https://doi.org/10.1088/2053-1583/ac5d0f

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Abstract

Much effort has been made to modify the properties of transition metal dichalcogenide layers via their environment as a route to new functionalization. However, it remains a challenge to induce large electronic changes without chemically altering the layer or compromising its two-dimensionality. Here, a non-invasive technique is used to shift the chemical potential of monolayer MoS2 through p- and n-type doping of graphene (Gr), which remains a well-decoupled 2D substrate. With the intercalation of oxygen (O) under Gr, a nearly rigid Fermi level shift of 0.45 eV in MoS2 is demonstrated, whereas the intercalation of europium (Eu) induces a metal–insulator transition in MoS2, accompanied by a giant band gap reduction of 0.67 eV. Additionally, the effect of the substrate charge on 1D states within MoS2 mirror-twin boundaries (MTBs) is explored. It is found that the 1D nature of the MTB states is not compromised, even when MoS2 is made metallic. Furthermore, with the periodicity of the 1D states dependent on substrate-induced charging and depletion, the boundaries serve as chemical potential sensors functional up to room temperature.

Highlights

(Eu) induces a metal-insulator transition in MoS2, accompanied by a giant band gap reduction of 0.67 eV
We have demonstrated a non-invasive method to strongly modify the electrostatic environment of ML MoS2, applicable to other transition metal dichalcogenide (TMDC) and van der Waals materials
We have shown that the doping of its Gr substrate can induce a metal-insulator transition in MoS2 and enables the manipulation of metallic states within mirror-twin boundaries (MTBs)

Summary

Introduction

(Eu) induces a metal-insulator transition in MoS2, accompanied by a giant band gap reduction of 0.67 eV. With this method, transport measurements showed that MoS2 and WS2 become superconducting when the chemical potential lies within the conduction band 9–14. Many open questions remain on the nature of the superconducting dome in MoS2 9–11,18,19 and WS2 13, the origin of the finite density of states within the superconducting gap 20, and on the properties of the (quasi-) metallic phase in between the insulating and superconducting phases 13 Another method to obtain large shifts of the chemical potential is the introduction of foreign species. An efficient method able to tune the chemical potential of TMDCs by large amounts without chemically altering it or leaving the surface inaccessible would be highly desirable Such a method would make it possible to monitor the effect of charge on the band structure of TMDC semiconductors 14, enabling access to novel phases of matter, such as topological superconductivity 28

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